Direct current high-voltage gas-insulated switchgear assemblies (DC GIS) of voltages up to ±550 kV are now readily developed and entering the market. With respect to current project developments coping with certain requirements of limited space in offshore HVDC converter platforms, onshore HVDC converter stations and transition stations between different transmission media, such as DC cables, DC overhead-lines and DC gas-insulated lines (DC GIL), DC GIS provide a compact technical solution with a high functional density.
Development and dimensioning of gas-insulated DC systems require distinct knowledge of the electric field distribution in the gas-solid insulating system dependent on the relevant influencing factors. Intensive research on this field during the last years shows a growing understanding of the basic characteristics of DC insulation.
Gas-insulated technology for direct current applications has been investigated since the 1960s with few applications worldwide. In the last years, development programs in Asia and Europe have made great progress in basic knowledge of DC gas-insulated systems, resulting in new technical solutions and commercial projects that are under preparation now.
The application potential of DC GIS for converter and transition stations is shaped by the modular design, allowing flexible arrangements even for complex station layouts. It is driven by the demand for space-saving installations with a high visual amenity and resilience.
This paper states the physical and technical background to design and develop compact DC switchgear assemblies using gas-insulated technology. It explains the developed modules of the substation, gives an overview of the performed tests and standardization activities and describes possible applications.